Conventional loudspeaker radiation patterns have no relationship to those
of the sound sources which they purport to simulate [Causse et al., Proceedings
of I.S.M.A. Tokyo, 67--70 (1992)]. In this particular study, the perceptual
difference between a real instrument and a programmable radiation pattern
loudspeaker system (12 independently programmable loudspeakers mounted on a
polyhedral structure) was investigated. In a first experiment, the trombone was
chosen for its radiation pattern which presents a cylindrical symmetry and a
monotonic variation according to frequency. For purposes of reproducibility
during perceptive tests, the programmable radiation pattern loudspeaker was
compared with an artificially driven trombone: The musical material was
recorded just after the U-bend of the bell joint. This signal was reproduced by
a driver, corrected by inverse filtering techniques, and mounted at the same
location. To supply the programmable radiation pattern loudspeaker system,
close-microphone recordings on axis and off axis were used. The programmable
loudspeaker was controlled with the help of filtering processes that were
calculated from previous measurements on the radiation pattern of the trombone.
Results of the listening tests will be presented and discussed.